Add autosave utilities

app/assets/javascripts/lib/utils/autosave.js

+export const clearDraft = autosaveKey => {
+  try {
+    window.localStorage.removeItem(`autosave/${autosaveKey}`);
+  } catch (e) {
+    // eslint-disable-next-line no-console
+    console.error(e);
+  }
+};
+
+export const getDraft = autosaveKey => {
+  try {
+    return window.localStorage.getItem(`autosave/${autosaveKey}`);
+  } catch (e) {
+    // eslint-disable-next-line no-console
+    console.error(e);
+    return null;
+  }
+};
+
+export const updateDraft = (autosaveKey, text) => {
+  try {
+    window.localStorage.setItem(`autosave/${autosaveKey}`, text);
+  } catch (e) {
+    // eslint-disable-next-line no-console
+    console.error(e);
+  }
+};

spec/frontend/lib/utils/autosave_spec.js

+import { clearDraft, getDraft, updateDraft } from '~/lib/utils/autosave';
+
+describe('autosave utils', () => {
+  const autosaveKey = 'dummy-autosave-key';
+  const text = 'some dummy text';
+
+  describe('clearDraft', () => {
+    beforeEach(() => {
+      localStorage.setItem(`autosave/${autosaveKey}`, text);
+    });
+
+    afterEach(() => {
+      localStorage.removeItem(`autosave/${autosaveKey}`);
+    });
+
+    it('removes the draft from localStorage', () => {
+      clearDraft(autosaveKey);
+
+      expect(localStorage.getItem(`autosave/${autosaveKey}`)).toBe(null);
+    });
+  });
+
+  describe('getDraft', () => {
+    beforeEach(() => {
+      localStorage.setItem(`autosave/${autosaveKey}`, text);
+    });
+
+    afterEach(() => {
+      localStorage.removeItem(`autosave/${autosaveKey}`);
+    });
+
+    it('returns the draft from localStorage', () => {
+      const result = getDraft(autosaveKey);
+
+      expect(result).toBe(text);
+    });
+
+    it('returns null if no entry exists in localStorage', () => {
+      localStorage.removeItem(`autosave/${autosaveKey}`);
+
+      const result = getDraft(autosaveKey);
+
+      expect(result).toBe(null);
+    });
+  });
+
+  describe('updateDraft', () => {
+    beforeEach(() => {
+      localStorage.setItem(`autosave/${autosaveKey}`, text);
+    });
+
+    afterEach(() => {
+      localStorage.removeItem(`autosave/${autosaveKey}`);
+    });
+
+    it('removes the draft from localStorage', () => {
+      const newText = 'new text';
+
+      updateDraft(autosaveKey, newText);
+
+      expect(localStorage.getItem(`autosave/${autosaveKey}`)).toBe(newText);
+    });
+  });
+});